Manufacture of moulded articles

ABSTRACT

A method is provided whereby the three components (sidewalls and tread) of a pneumatic tire are moulded in a single press operation using two transfer units charged with uncured rubber which are located in the press so as to discharge to the mould cavities when the press is closed, after which the press is opened to allow removal of the transfer units, (the moulded components remaining in the press) and then reclosed to assemble the components together. Each transfer unit comprises at least one reservoir for uncured rubber defined between parts of the unit which are relatively movable under the action of the press to transfer the rubber from the reservoir(s) to associated mould cavities.

This is a division of application Ser. No. 665,429, filed Mar. 10, 1976,now U.S. Pat. No. 4,006,053.

The present invention relates to an improved method and apparatus formoulding articles, such as pneumatic tires.

In accordance with one aspect of the present invention there is provideda method of producing a moulded article from a plurality of components,comprising locating in a press a transfer unit assembly incorporatingmould surfaces which together with co-operating surfaces or die membersof the press form mould cavities for the components, said transfer unitassembly having at least one transfer reservoir between relativelymovable parts of the unit charged with mouldable material, closing thepress to cause relative movement of said parts which will effecttransfer of the material from the transfer reservoir or reservoirs tothe cavities to form all of the said components in a single pressoperation, opening the press and removing the transfer unit assemblywhilst leaving the moulded components on the die members and re-closingthe press to bring the components supported on the die members intoassembled relationship and to bond the components together.

In accordance with another aspect of the present invention there isprovided a method of moulding a pneumatic tyre having sidewalls joinedby a tread portion the method comprising:

Locating at a filling station two transfer units, each unit comprisingin its face remote from the other transfer unit a mould surface for oneof the sidewalls, each unit comprising at least two parts relativelymovable axially of the unit between an open position in which the volumeof at least one reservoir for uncured rubber defined between said partsis relatively large and a closed position in which said volume isrelatively small, and passageways means communicating the axiallyopposite faces of each unit with a reservoir thereof,

Charging the reservoirs of the transfer units with mouldable material atthe filling station,

Opening a press so that sidewall die members thereof are relativelyspaced, the faces of the sidewall die members presented toward oneanother comprising mould surfaces for the sidewalls and locking spuegrooves adjacent the mould surfaces,

Locating the transfer units in the press so they are positioned betweenthe sidewall die members with the sidewall mould surfaces of thetransfer units presented towards the mould surfaces of the sidewall diemembers,

Closing the press whereby a mould cavity for the tread portion isdefined between the transfer units and a mould cavity and locking spuegroove for one of the sidewalls is defined between each sidewall diemember and the mould surface of the adjacent transfer unit, each saidcavity communicating with a passageway of at least one of the transferunits,

applying pressure to the closed press relatively to move the parts ofeach transfer unit to the closed positions thereof whereby mouldingmaterial is transferred from the reservoirs to the cavities via thepassageways,

re-opening the press and removing the transfer units therefrom, themoulded tread portion remaining in the press and the moulded sidewallsbeing held on the respective sidewall die members by the moulded lockingspues and

re-closing the press to bring the moulded sidewalls, held by the lockingspues, into contact with the moulded tread portion on opposite sides ofthe latter and bonding the sidewalls to the tread portion, the methodadditionally comprising subjecting the moulding components of the pressto superatmospheric pressure during the moulding operation andsubsequent bonding operation.

The pressurization serves to prevent gassing off from the warm compoundafter moulding and, particularly in moulding the sidewalls acts inconjunction with the locking spues to keep the moulded part in thecorrect part of the mould for the joining to be carried out. It will benoted that gassing off from the warm compound is particularlyundesirable since it gives rise to ugly pitting of the surface of themoulded tire part and gives rise to porosity in the finished productwhich can lead to structural failure of the tire in use.

The rubber may be any elastomeric, cross-linkable polymeric material,for example natural rubber, butyl rubber, SBR, neoprene,ethylene-propylene rubber and nitrile rubber or mixtures thereof. Thetype of rubber used will of course depend on the desired properties ofthe finished tire and the selection and compounding of a suitable rubberfor any particular purpose is a well-known procedure in the field ofrubber technology.

Although the rubber is to be substantially uncured when used to form theparts of the tire, it is preferred to subject it to a certain amount ofworking prior to the forming steps in order to destroy its "nerve" or"memory". Suitable working may be, for example, by milling, extrusion orother mechanical or heat treatment but should not be sufficient to startthe rubber on its curing cycle. In other words, although the rubber mayhave been subjected to a certain amount of energy, it is stillsubstantially uncured when used to form the tire parts.

The press preferably comprises an intermediate die member adapted toprovide a mould cavity for the tread portion and positioned between thesidewall die members in the press, the arrangement being such that inthe operative positions of the transfer units each is located betweenthe intermediate die member and a respective one of the sidewall diemembers. The intermediate die member preferably comprises at least twoparts which are separable when the press is open to permit theintroduction of a breaker structure into the mould cavity for the treadportion. In the moulding of the tread portion, the tread pattern willserve the same purpose as the locking spues on the sidewalls.Pressurization of the tread portion will maintain intimate contactbetween the tread and the tread pattern of the intermediate die memberand will prevent gassing off from the warm tread rubber.

Each transfer unit preferably comprises three parts defining tworeservoirs for moulding material, the reservoirs communicatingrespectively with the sidewall mould surface and the tread portion mouldsurface of the transfer unit. The transfer units are preferablyremovable from the press to filling positions at a filling station wheremeans is provided for charging the reservoirs of the transfer unitswhich mouldable material. This means is preferably adapted to introducedifferent mouldable materials into the two reservoirs of each transferunit and may take the form of a single distribution member at thefilling station capable of discharging to both transfer units when theyare positioned on its opposite sides.

A preferred embodiment of the invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a front elevation, partly in section and with parts cut away,of apparatus for carrying out the method of the invention;

FIG. 2 is a side elevation partly in section of the apparatus of FIG. 1viewed in the direction of arrows II--II;

FIG. 3 is a side elevation partly in section, as viewed in the directiontaken on the line of arrows III--III of FIG. 1;

FIG. 4 illustrates in sectional elevation and in perspective the twotransfer units of the apparatus of FIGS. 1 to 3, the associated part ofthe filling press and the associated centering apparatus;

FIG. 5 is a perspective view of the bottom part of the apparatus ofFIGS. 1-3;

FIG. 6 illustrates a breaker support ring or former used in the press ofFIGS. 1 to 3;

FIG. 7 illustrates the same former inside a finished tire manufacturedby the apparatus of FIGS. 1 to 3, and

FIGS. 8 to 14 schematically illustrate the machine of FIGS. 1 to 3during the different stages of the manufacturing process.

The machine illustrated comprises a main press 10 and a filling press 11which are located in side-by-side relation between a common head bolster12 and a common base 13 joined at the four corners of the machine andbetween the main and filling presses by six circular-section columns 14.The main press comprises an upper unit 15 and a lower unit 16 bothguided for vertical movement toward and away from one another and havingintegral with their opposed faces respective sidewall mould parts 17 and18. As described in the Assignee's U.S. Pat. No. 3,825,457 of July 23,1974, the sidewall mould parts 17 and 18 have mould surfaces adjacentwhich are locking spue grooves (not shown) shaped to mould spues of thekind illustrated in FIG. 7.

In FIG. 7 a moulded tire part 100 is shown having a spue 121 on one ofits sidewall portions. Spue 121 is so shaped that pressurized gasintroduced into the mould will deflect over the spue and thereby willnot get between the moulded part and the surface of the mould itself,i.e. the tendency for the gas to get between the exterior of thefinished product of the moulded part and the surface of the mould itselfis effectively reduced.

The upper unit 15 is arranged to be driven downwardly by an hydraulicram 19 and to be raised by pull back rams 20 while the lower unit 16 isarranged to be raised and lowered by a bottom hydraulic ram unit 21(FIG. 2). In operation of the main press, most of the daylight is takenup by the relatively long stroke bottom ram 21, whereupon the bottomunit 16 is locked against downward movement by operation of the"dog-clutch" arrangement best illustrated in FIG. 5 and which isactuated by the hydraulic ram 22. The comparatively short-stroke mainram 19 is now operated to apply full press pressure. The lower unit 16is surrounded by a pressure sealing skirt 23 and at its lower end hascircumferentially spaced load blocks 24. When the circular-section unit16 is raised by the ram 21 the load blocks 24 rise above a crown-shapedmember 25 controlled by the ram 22. The member 25 consists of a circularbase 26 on and rotatable relative to the base 13 and circumferentiallyseparated upstanding teeth 27. After the unit 16 has been raised abovethe member 25 by the ram 21 the ram 22 is actuated to rotate the member25 so that its teeth 27 come into alignment with the load blocks 24. Inthis position it is not possible for the unit 16 to descend because theload blocks 24 rest on the tops of the teeth 27. When it is desired tolower the unit 16 the load blocks 24 are first raised clear of the teeth27 by the ram 21, the ram 22 is actuated to rotate the member 25 untileach tooth 27 is between two of the load blocks 24 and thereafter theram 21 can be actuated to cause the unit 16 to descend, the teeth 27 ofthe member 25 passing between adjacent load blocks 24. In this way thegreater part of the daylight of the press is taken up by a prolongedmovement of the unit 16 which is then locked and thereafter presspressure is applied by the short stroke ram 19 to the upper unit 15.When opening the main press the pull back rams 20 are used to displacethe upper unit 15 upwardly.

In addition to the sidewall die members 17 and 18 the main pressincludes a two-part intermediate die member 28 which is located forvertical movement by pillars 29 of the main press. When closed, theintermediate die member is dimensioned to receive the annular treadformer or breaker support ring illustrated in FIGS. 6 and 7 and formtherewith a mould cavity for the tread portion of a pneumatic tire.

The filling press comprises a fixed upper unit 31 to which a top heatsink 32 is secured and a lower unit 33 to which a bottom heat sink 34 issecured and which is vertically displaceable by an hydraulic clampingram 35. Two rubber feed screws 36 penetrate the head bolster 12 at thefilling press and are connected by respective feed channels 37 and 38(see FIG. 3) to a distribution plate 39 in a central position in acentral position in the filling press. The distribution plate 39 has anormal position (FIG. 9) from which it can be raised (FIG. 8) by theaction of the ram 35. The feed screws 36 incorporate sliding seals (notshown) whereby the vertical displacement of the plate 39 can beaccommodate without interrupting the feed channels.

Extending between the main and filling presses are two pairs ofhorizontally aligned runways 42 and 43 each in the form of a horizontalslide of low friction material. Each slide is engaged by a bracket 40 or41 forming part of a carriage frame for an associated transfer unit 44or 45. Suitable drive means is provided for independently displacingeach of the transfer units 44 and 45 between an operative position inthe main press and an inoperative position in the filling press. Thetransfer units are shown in the latter position in FIGS. 1, 3 and 8. Thedrive means may take the form of hydraulic cylinders (not shown)anchored to frame parts of the press fast with the head bolster 12. Inthe operative positions of the transfer units (FIGS. 10 and 11) theupper unit 44 is between the upper sidewall die member 15 and theintermediate die member 28 and is displaceable therefrom to aninoperative position (FIGS. 8, 9, 12, 13 and 14) in the filling pressbetween the upper heat sink 32 and the distribution plate 39.Independently of the upper transfer unit 44 the lower transfer unit 45is movable between an inoperative position in the filling press betweenthe lower heat sink 34 and the distribution plate 39 (FIGS. 1-3, 8, 12,13 and 14) and an operative position in the main press (FIGS. 9-11)between the intermediate die member 28 and the lower sidewall die member16.

As is more clearly shown in FIG. 4, each transfer unit 44 and 45 is ofthree part construction including a central plate 46 or 47 in theopposite faces of which annular channels 48, 49, 50 and 51 are formed.In each channel a respective piston plate 52, 53 and 54, 55 is locatedto be axially displaceable relative to the central plate 46 or 47 andeach central plate has oppositely extending central bosses 56, 57 and58, 59 which locate in corresponding central bores in the piston plate.The distribution plate 39 is formed with central areas 60 and 61 shapedrespectively to fit the exposed face 62 of the piston plate 53 and theexposed face 63 of the piston plate 54. Individual channels 64 and 66 inthe distribution plate 39 respectively communicate with the screwfeeders 36 (see FIG. 3), the passageway 64 branching to the oppositeaxial faces of the plate 39 at the centres of the formations 60 and 61and the passageway 66 branching to the opposite faces of the plate 39nearer to the peripheries of the formations 60 and 61. In this way thedownstream ends of the passageway 64 communicate, when the filling pressis closed, with central passageways 65 and 67 in the respective transferunits and these in turn communicate via runners 68 in the central plateof each transfer unit with annular reservoir areas or pots 69 and 70 ofthe transfer units. Similarly the downstream ends of the passageway 66in the distribution plate communicate with runners in the adjacent parts53 and 54 of the transfer units which in turn communicate with secondpots 71 and 72.

It will be clear that on closure of the filling press by actuation ofthe ram 35 first the "daylight" between the transfer unit 45 and thedistribution plate 39 is taken up and thereafter the "daylight" betweenthe plate 39 and the transfer unit 44. As it is undesirable that contactbetween some press parts should occur before others, because of thedanger of displacement of the contacted parts by those coming intocontact, centering apparatus is provided in the form of hydraulicpistons 130 projecting from bosses 131 on the face of the transfer unit45 presented to the distribution plate 39. Similar pistons 133 andbosses 134 (FIGS. 8-14) are provided on the face of transfer unit 44presented to the distribution plate 39 and these are arranged to locatein respective collars 132 on the upper face of the plate 39. Similarcollars 135 are fixed to the underside of the plate 39 respectively toreceive as a sliding fit the bosses 131.

The pistons 130, 133 are normally maintained in a fully extendedcondition out of the respective bosses 131, 134, as shown, by hydraulicfluid acted upon by pressurized air. As the filling press closes thebosses 131 on the lower transfer unit 45 enter the associated collars,135 to prevent any subsequent lateral displacement of the unit 45relative to the distribution plate 39. Air pressure resisting retractionof the pistons 130 into the bosses 131 prevents final closure of theunit 45 and plate 39 until bosses 134 on the unit 44 are also located inthe associated collars 132. Continued closure of the filling press afterthe pistons, 130, 133 of both units 44 and 45 are in contact with thedistribution plate 39 will cause simultaneous retraction of all of thepistons 130, 133 into the associated bosses 131, 134 so that during thefinal closing movement of the filling press not only is lateraldisplacement of each unit 44 and 45 relative to the plate 39 preventedby location of the bosses 134 in the collars 132 and bosses 131 in thecollars 135, but also the resistance to retraction of the pistons 130,133 ensures that both units come into contact with the distributionplate simultaneously.

The pistons 130 and 133 also contact the upper and lower surfaces of thetwo-part intermediate die member 28 when the transfer units arepositioned in the main press and the main press is closed. Thesimultaneous final closure of the die member parts 80 and 81 with thetransfer units 44 and 45 thus ensured is particularly important toprevent displacement of the breaker structure located between the parts80 and 81 as described below.

The main and filling presses are jointly surrounded by a rectangularpressure casing or shroud 73 which is vertically displaceable between anopen position shown in FIGS. 1 to 3 and a raised, closed position. Thepressure casing 73 has sliding seals 200 which form a seal with thecylindrical pressure sealing skirt 23 surrounding the ram 21 of the mainpress and a similar pressure sealing skirt 75 surrounding the ram 35 ofthe filling press. The upper periphery of the casing 73 is provided withanother pressure seal 76 and in the raised position of the casing 73this abuts a flange 77 surrounding the main and filling presses at theperiphery of a top part 201 of the casing fast with the head bolster 12.Suitable ram operated locking means 78 is provided for locking thecasing 73 in its raised positon with the seal 76 in engagement with theflange 77. The head bolster 12, flange 77, pressure casing 73 and skirts23 and 75 provide an openable enclosure for the main and filling pressespermitting them to be pressurised.

A super-atmospheric pressure is provided in the closed casing 73 by acompressor (not shown) to prevent "gassing-off" of the worn rubber andto hold the moulded tire parts in position on the dies. The screwfeeders 36, the distribution plate 39 and the heat sinks 32 and 34 areprovided with distribution channels (not shown) for a heating or coolingfluid medium for controlling the rate of cure of the rubber.

The operation of the press illustrated in FIGS. 1 to 3 will now bedescribed with reference to FIGS. 8 to 14.

With the pressure casing 73 lowered and the transfer units 44 and 45 intheir inoperative positions in the filling press the ram 35 is operatedto close the filling press and uncured rubber introduced through feedpassages 37 and 38 (FIG. 3) is driven by the screw feeders 36 throughthe passageways 64 and 66 in the distribution plate 39 and theregistering passageways in the transfer units into the two annular pots69, 70 and 71, 72 of the transfer units (FIG. 4). In this way a measuredquantity of uncured rubber is introduced into each pot, a differentcompound from a different one of the screw feeders 36 reaching therespective pots of each transfer unit.

On completion of the charging of both transfer units the ram 35 isretracting and lower transfer unit 45 is moved from the filling press tothe main press (FIG. 9) the pressure casing 73 remaining open so that anoperator standing on a platform adjacent the main press (not shown) hasaccess to the intermediate die member 28. The two component parts 80 and81 of the intermediate die member 28 are at this time separated andnon-rubber components of the tire, including a breaker structure 150mounted on a deformable breaker support ring 30 are located by theoperator between the two parts 80 and 81 of the intermediate die member,the assembly 150, 30 resting on the lower part 81 of the intermediatedie member. When located in the press the breaker support ring 30 mayalready have mounted on it the breaker structure 150 for the tire andmay be expanded within the press to stress the breaker structure 150 allas described the assignee's co-pending Patent Application Ser. No.579,424 of May 21, 1975, now U.S. Pat. No. 5,997,878. To improve itsdeformability the radially inner portion 135 of the breaker support ringmay be axially slotted as shown at 136 in FIG. 6. As also described inthe said provisional specification the breaker structure may have edgeportions tucked into inflatable pockets (not shown) of the former andmeans (not shown) may be provided for inflating these pockets at a laterstage of the process to engage the breaker structure 150 against thetire sidewalls. With the breaker structure on the former 30 mountedwithin the intermediate die member 28 its two parts 80 and 81 are closed(FIG. 10) so as to define with the former 30 an annular mould cavity 82for the tread portion of a pneumatic tire. As described in theAssignee's co-pending patent application Ser. No. 581,587 of May 28,1975 the cavity 82 communicates with a surrounding pot 83 definedbetween the two parts of the intermediate die member 28 and the pot 83communicates with the external surfaces of the closed intermediate diemember by runners 84.

The upper transfer unit 44 is now moved into the main press above theclosed intermediate die member, the pressure casing 73 is raised andlocked and pressurized air is introduced into the closed casing 73. Theram 21 is operated to close up the daylight of the main press, raisingthe lower transfer unit 45 and the intermediate die member 28 againstthe upper transfer unit 44 and with the ram 21 extended the ram 22 isactuated to rotate the crown member 26, thus preventing re-lowering ofthe members of the main press. This is shown in FIG. 5. The ram 19 ofthe main press is now operated (FIG. 11) to exert a downward pressure onthe upper sidewall die member 17 which is transmitted to the transferunits 44 and 45 and reacts against the lower sidewall die member 18which is prevented from descending by the crown member 27. The pressureapplied to the transfer units 44 and 45 by the main press ram 19 has theeffect of displacing the piston plates 52, 53 and 54, 55 of the transferunits inwardly of the respective center plates 46 and 47 so that thedimensions of the pots 69, 70, 71 and 72 are reduced. By this means afirst rubber compound is displaced from the pots 69 and 70 (FIG. 4) intosidewall mould cavities 85 and 86 defined between the exposed surface ofthe piston plate 52 of the transfer unit 44 and the upper sidewall diemember 17 of the press and between the piston plate 55 of the transferunit 45 and the lower sidewall die member 18 of the main press and intothe locking spue grooves (not shown) adjacent and opening to thesecavities. At the same time a second rubber compound is displaced fromthe pots 71 and 72 through the runners 84 of the intermediate die memberwhich are now in register with runners of the piston plates 53 and 54 ofthe transfer units into the annular pot 83 and thence into the mouldcavity 82.

Full pressure is maintained for a predetermined period to effect apartial cure of the compounds in their respective cavities andthereafter pressure applied by the main ram 19 is relieved.

The ram 21 is now re-actuated to lift the load blocks 24 clear of theteeth of the crown member 26 (see FIG. 5) whereupon the ram 22 isactuated to rotate the crown member unitl the teeth 27 are aligned withthe gaps between the load blocks 24. The ram 21 is now retracted fullyto open the main press. Because of their locking spues the moulded tiresidewalls 100 and 101 are not dislodged from their moulded positions onthe main press sidewall die members 17 and 18 and the moulded tire treadportion 102 remains in the mould cavity between the two parts of theintermediate die member 28. A tread-forming pattern on the intermediatedie member assists in retaining the tread portion thereon.

With the transfer units 44 and 45 clear of the die members 17, 18 and 28of the main press they are both moved from the main press to the fillingpress (FIG. 12). It is to be appreciated that all this time the pressurecasing 73 remains closed and pressurized and thus assists in retainingthe three, annular moulded tire portions 100, 101 and 102 in position onthe respective die members. With the transfer units clear of the mainpress the ram 21 is now fully extended above the teeth of the crownmember until the radially outer ends of the tire sidewalls 100 and 101are brought into contact with the opposite axial ends of the tread 102by the sidewall die members 17 and 18 of the main press abuttingopposite sides of the intermediate die member 28 (FIG. 13). Thisproduces a fully assembled pneumatic tire although subsequent operationsmay be performed to join the breaker structure 150 surrounding theformer 30 and now embedded in the tread 102 of the tire with anysidewall reinforcing plies which may have been provided, e.g. byinflating pockets (not shown) in the former 30 to displace the breakeredges into contact with the tire sidewalls as described in theprovisional specification of the Assignee's previously mentionedco-pending patent application Ser. No. 579,424.

The closed casing 73 is now gradually depressurized by opening a reliefvalve (not shown) during a predetermined cure period for the finishedtire, during which pressure on the main press die members 17, 18 and 28is maintained by the rams 19 and 21.

At the end of the full cure cycle, the casing 73 having been fullydepressurized, the ram 19 is de-actuated and the upper die member 17raised by the pull back rams 20. At the same time the ram 21 isretracted to lower the bottom main press die member 18, the sidewalls100 and 101 of the finished tire separating from the die members 17 and18 because of their bonding to the tread portion 102 of the tire and thelocking spues on the sidewalls being dislodged from their associatedrecesses in the sidewall die members 17 and 18 because of the superiorstrength of the bond between the sidewalls and tread portion of thefinished tire (FIG. 14). The two parts 80 and 81 of the intermediate diemember 28 are vertically separated to expose the finished tire and thedepressurized casing 73 is lowered to provide access by the operator tothe interior of the main press.

With the main press fully open, the casing 73 fully lowered and the twoparts 80 and 81 of the intermediate die member 28 fully separated theoperator can remove the finished tire from the press with the deformablebreaker support ring 30 within it. It then remains to trim off thelocking spues and the annular spue 104 produced by the annular pot 83 ofthe intermediate die member 28 and the associated runners of theintermediate die member and to pull the deformable breaker support ring30 out of the finished tire as described in patent application Ser. No.579,424. During removal of the finished tire from the main press the ram35 of the filling press is actuated to engage the transfer units 44 and45 with the heat sinks 31 and 34 and with opposite sides of thedistribution plate 39 to recommence the cycle of operations alreadydescribed for the manufacture of a second tire.

Although in the preferred embodiment of the invention above describedthe tire-forming process is carried out under super-atmospheric pressurethis is not essential to the invention. It is contemplated that by usingsuitable rubber mixture under suitable temperature conditions thepressure casing 73 and associated skirts 21 and 75 could be dispensedwith.

Also although in the preferred embodiment of the invention abovedescribed rubber for the sidewalls and the tread of the tire isintroduced into the transfer unit at the filling press it iscontemplated that the transfer units should be charged at the fillingpress only with rubber for the sidewalls, or alternatively only withrubber for the tire tread portion, and that rubber for the tread portionof the tire, or alternatively for the sidewalls, should be introduceddirectly to the appropriate components of the main press. For example,if the tread portion rubber is introduced directly by a screw-feeder(not shown) to the intermediate die member 28 of the main press each ofits components 80 and 81 will comprise relatively axially movable partsdefining an annular pot therebetween communicating via suitable runnerswith the cavity 82 on the one hand and with a screw-feeder on the otherhand.

Alternatively the die members 17 and 18 of the main press may be oftwo-part construction defining an annular pot therebetween whichcommunicates via runners on the one hand with thesidewall-cavity-defining surfaces 85 and 86 of the die members 17 and 18and on the other hand with a screw-feeder for rubber compound.

In either of these alternative arrangements rubber compound will beintroduced into the charging cavity or pot between the part of the mainpress by the associated screw-feeder and thereafter on closure of themain press the measured rubber compound will be displaced from the potor pots into the tire-forming cavity or cavities defined between mainpress parts and the transfer units located therein.

Having now described my invention -- what I claim is:
 1. A method ofmoulding a pneumatic tire having sidewalls joined by a tread portion themethod comprising:locating at a filling station two transfer units, eachunit comprising in its face remote from the other transfer unit a mouldsurface for one of the sidewalls, each unit comprising at least twoparts relatively movable axially of the unit between an open position inwhich the volume of at least one reservoir for uncured rubber definedbetween said parts is relatively large and a closed position in whichsaid volume is relatively small, and passageway means communicating theaxially opposite faces of each unit with a reservoir thereof, chargingthe reservoirs of the transfer units with moulding material at thefilling station, opening a press so that sidewall die members thereofare relatively spaced, the faces of the sidewall die members presentedtoward one another comprising mould surfaces for the sidewalls andlocking spue grooves adjacent the mould surfaces, locating the transferunits in the press so they are positioned between the sidewall diemembers with the sidewall mould surfaces of the transfer units presentedtowards the mould surfaces of the sidewall die members, closing thepress whereby a mould cavity for the tread portion is defined betweenthe transfer unit and a mould cavity and locking spue groove for one ofthe sidewalls is defined between each sidewall die member and the mouldsurface of the adjacent transfer unit, each said cavity communicatingwith a passageway of at least one of the transfer units, applyingpressure to the closed press relatively to move the parts of eachtransfer unit to the closed positions thereof whereby moulding materialis transferred from the reservoirs to the cavities via the passageways,re-opening the press and removing the transfer units therefrom, themoulded tread portion remaining in the press and the moulded sidewallsbeing held on the respective sidewall die members by the moulded lockingspues and re-closing the press to bring the moulded sidewalls, held bythe locking spues, into contact with the moulded tread portion onopposite sides of the latter and bonding the sidewalls to the treadportion, the method additionally comprising subjecting the mouldingcomponents of the press to superatmospheric pressure during the mouldingoperation and subsequent bonding operation.